Silver copper alloy



Patented Apr. 9, 1940 UNITED STATES PATENT OFFICE SILVER COPPER ALLOY No Drawing. Application February 21, 1939, Serial No. 257.667

4 Claims. (Cl- 75-1'13) This invention relates to a new silver alloy for use as replacement of pure silver and for all uses to which previously known silver alloys have been employed, of whichmay be mentioned par- 5 'ticularly, uses of the alloys of the present invention in connection with silver solders, electrical contacts, silverware, jewelry and dental applications.

It is one object of the present invention to provide an alloy which has improved electrical properties such as electrical conductivity.

It is a further object of the present invention to provide an alloy which shows great fluidity in the molten state and lends itself to casting of very intricate shapes.

It is a further object of the present invention to produce an alloy which has improved wetting.

characteristics when used as a silver solder.

A still further object is to produce a new alloy which has superior electrical characteristics when used as an electrical make-and-break contact such as low material transfer, low contact resistance and freedom from welding or sticking. Other objects .of the invention will be apparent from the following description taken in connection with the appended claims. The present invention comprises the combination of elements, methods of manufacture and the product thereof brought out and exemplified in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.

While a preferred embodiment of the invention is describedherein, it is contemplated that considerable variation may be made in the method of procedure and the combination of elements without departing from the spirit of the invention.

The present invention contemplates the addiv40 tion of lithium and copper to silver base alloys.

In the formation of the alloy it is preferable to provide a composition of the materials specified in the following proportions by weight:

Percent Lithium .002 to 3 Copper .1 to 75 Balance substantially all silver.

A number of preferred compositions are given We have also found that ,the following elements 16 may also be added to improve the characteristics of the new alloys of the present invention:

Percent Cadmium Up to 25 Zinc Up to-28 2o Tin Up to 11 Manganese Up to 20 Nickel Up to 10 Phosphorus Up to 8 Silicon. Up to 2 :5 Magnesium Up to 8 Beryllium Up to 3 Calcium Up to 2 In addition to these baser elements, materials from the palladium, platinum or gold group may also be present up to 10% each.

The alloys of the present invention may be prepared by melting the ingredients together in the correct proportions. The lithium is preferably added in the form of a silver-lithium 35 master alloy, containing approximately 15% of lithium. This master alloy has a very low melting point which is in the neighborhood of 410 to 450 C. and therefore will go readily into solution when .added to the silver-copper melt.

The effect of lithium is to completely deoxidize the silver melt and to free it from other impurities which are harmful. Part of the lithium will be eliminated together with these impurities and the remaining melt 'will be free from in- 45 clusions and oxides. The presence of lithium also prevents the further oxidation of the melt during the heating periods to which the melt may be subjected and the material retains a very high fluidity during pouring, resulting in extremely 5 clean castings. I

We have found that'sterling silver or coin silver containing a small percentage of lithium such as, for instance, 0.1% or less will lend itself much more readily to rolling and wire drawing operations, resulting in a material which is entirely free from surface blemishes and oxide stringers. Furthermore if such silver wire is being spun or if silver wire produced in that manner is being headed a surface finish can be obtained with alloys of the new invention that excels anything obtainable so far with alloys of the prior art. Very often in heading of coin silver or sterling silver wire the formation of edge cracks or splits is encountered, causing a great number of rejects. By using the addition of lithium in these alloys in the proportions specified these difliculties can be eliminated or at least materially reduced.

If lithium is used in higher proportions such as .05 to 1% we have found that alloys of the coin silver or sterling silver type or alloys containing copper as low as 0.5 to 1% will show greatly improved electrical characteristics. Contact alloys of this type have very improved characteristics as far as material transfer and contact resistance are concerned. It was also of great interest to find that the material transfer for this composition was from the cathode to the anode. In most silver base alloys the material transfer is in the opposite direction, therefore it seems desirable to use the material of the present invention in combination with another silver alloy having opposite transfer characteristics. We have carried out a large number of experiments with compositions of this type in which the eutectic silver-copper combination of 28.5% copper, balance silver was used as a base. To this material was added approximately 25% of lithium and the material was then rolled into sheet or drawn into wire to be used for silver soldering purposes. It was found that alloys of such a composition would give most excellent results as far as wetting characteristics and strengths were concerned. Materials of this type were compared with the silver-copper-phosphorus combinations and it was found that greatly improved joints could be produced by using a small percentage of lithium instead of phosphorus. It

was also possible, however, to improve the commercial silver-copper-phosphorus alloys by using an additonal amount of lithium, such as .01 to 5%.

Since lithium decreases the melting point of silver very materially and since an eutectic is formed at 2.7% lithium, having a melting point of 610 C. care must be exercised if these materials are being processed at elevated temperatures and if they contain higher percentages of lithium. By proportioning the ingredients correctly the materials can be easily processed into desirable forms. We have also found that the addition of other elements, which are usually employed in silver-copper base alloys such as cadmium to improve the contact performance or tarnish resistance or zinc which improves the tarnish resistance or manganese which improves the fluidity or nickel which improves the strength and the like can be made to the alloys of the pre-'- ent invention in order to provide materials for certain specific purposes, particularly for certain silver solders.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An alloy containing .1 to 35% copper, .002 to 3% lithium, balance substantially all silver.

2. An alloy containing about 10% copper, about .002 to 25% lithium, balance substantially all silver.

3. An alloy containing about 28% copper, about .002 to 1% lithium, balance substantially all silver.

4. An alloy containing about 28% copper, about 2.5% lithiumfbalance substantially all silver.

FRANZ R. HENSEL. KENNETH L. EMMERT. JAMES W. WIGGS. 

